Is there any way of calculating, from the above results, how close he is to reaching the magic 1000 mark?

You would need to know or estimate the strength of the opposition.

The easy bit is 4.5/9 as the opposition is equivalent to the rating performance ie 9 * 1233

For the rest of them, the rating has to be at least 1000 to count. Otherwise you work from the tables in the FIDE rating manual on the FIDE website. Unless he scores at least 50%, the average opposition has to be above 1000 to get a rating. The exact method used for new ratings is also in the rating manual.

In English chess, it's not normally the practice to FIDE rate tournaments where the participants are around the 1000 standard. The lowest rated player in the next 4NCL tournament is just under 1500.

If Rp stands for performance rating then Sum(nxRp)/Sum(n) should give his current "rating".
This gives 40223/43 = 935.

His early results (910, 286, 300) are very poor so he needs to overcome those, which he can do in two ways.

The first involves doing well in more tournaments to bring his average performance up to 1000. As he is probably improving anyway this is the obvious way to go.

The second involves waiting until those early results go out of "scope". I think results have a lifetime of something like 26 months (sorry I'm too lazy, had too much wine to check). If that's correct and he plays no chess until the end of 2019 then he would have a rating of 1059.

If Rp stands for performance rating then Sum(nxRp)/Sum(n) should give his current "rating".
This gives 40223/43 = 935.

His early results (910, 286, 300) are very poor so he needs to overcome those, which he can do in two ways.

As opponents must have a rating of at least 1000 to be included and there's a 400 point cut off, I rather think the scores of 286 and 300 would count for rather more when combined with better results.

That's a very good point, Roger.

The 286 and 300 scores are based on all losses (i.e. -800 for a loss) rather than 400. Making the adjustment gives 42623/43 = 991. That would suggest one more decent performance (say 1050 over 9 rounds) should push him over the 1000 mark.

This boy is very keen on chess! He has just started another rating tournament - the Tamil Nadu State Sub-Junior Championship (for children under 15 years) and has won his first round against a 1252-rated player. So hopefully he will get over the 1000 mark this time.